Browse Prior Art Database

AUTOMATIC DC OFFSET ADJUSTMENT FOR A STEPPER MOTOR CONTROLLER

IP.com Disclosure Number: IPCOM000026636D
Original Publication Date: 1993-Feb-28
Included in the Prior Art Database: 2004-Apr-06
Document File: 4 page(s) / 177K

Publishing Venue

Xerox Disclosure Journal

Abstract

In the controller for the stepper motor of a raster input scanner, a SETPOINT SIGNAL specifies the desired current that is to be maintained in the motor phase winding. Using a closed loop current control, the motor is stepped by varying the SETPOINT in a prescribed manner. In the ensuing discussion, the SETPOINT waveforms (and thus the actual current) for the phase windings are sinusoids in quadrature.

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XEROX DISCLOSURE JOURNAL

AUTOMATIC DC OFFSET Proposed Classification ADJUSTMENT FOR A STEPPER
MOTOR CONTROLLER
Thomas Davis

U.S. C1.318/635 Int. C1. G05B 11/01

CURRENT CONTROL LOOP

Ref.

-

XEROX DISCLOSURE JOURNAL - Vol. 18,So. 1 Januarp/February 1993 13

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Page 2 of 4

AUTOMATIC DC OFFSET ADJUSTMENT FOR A STEPPER MOTOR CONTROLLE R(Cont'd)

1

I Setpoint Signal I

-------

L,, 1----

10 I

        I Setpoint f

(09

MOTOR PHASE

Voltage +

Circuit

8031 Correction ~

7 r--'-- 1 I

Voltage ++

Circuit

I I

DC Offset

I

 Null I 1 ; Detect

   r----- I I - I I I --I Errorsignal I -

------

1 - I Sensed Current Signal I

I Correction I ---------- I I DCOffset 1 1 - - - - - - - - - - I Signal I

I------

FIG. 2

14 XEROX DISCLOSURE JOC'RNAL - Vol. 18: 50. 1 January/February 1993

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Page 3 of 4

AUTOMATIC DC OFFSET ADJUSTMENT FOR A STEPPER MOTOR C ONTROLLE R(Cont'd)

In the controller for the stepper motor of a raster input scanner, a SETPOINT SIGNAL specifies the desired current that is to be maintained in the motor phase winding. Using a closed loop current control, the motor is stepped by varying the SETPOINT in a prescribed manner. In the ensuing discussion, the SETPOINT waveforms (and thus the actual current) for the phase windings are sinusoids in quadrature.

The input offset voltage of the op-amps associated with the current control loop as well as the individual component tolerances, combine to produce a DC offset in the phase current of the motor. Here DC offset in the phase current is defined as that current present in the phase winding when the controller specifies that zero current be maintained in the phase. This DC offset manifests itself as a non-incremental positional error in the stepping of the motor which potentially could degrade the motion quality of the scanner to the point where undesirable effects are introduced into the scanned image.

In order to avoid degradation of the motion quality of the scanner, it is desirable that the magnitude of the DC offset be held to within 1% of the peak phase current (approximately 20 mA). While this could be accomplished using very high precision, tight toleranced components, the cost would probably be unacceptable. A more viable solution would be to first sense for the presence of significant DC offset, and then adjust the phase current appropriately to compensate for it. The primary intent is to maintain a current in the motor phase winding proportional to the SETPOINT SIGNAL generated by the control software.

Referring to Figure 1, because of the negative feedback, the current control loop there shown will stabilize when the ERROR SIGNAL goes to zero. This can only occur when the desired current level (specified by the SETPOINT SI...